Lost&Found Videothek is the concept for an interactive video library thought for users engaged in an exploratory research mode, in which content is organized according to a collaborative, subjective and implicit indexing system for the enhancement of serendipity. This idea was the result of a design-based research with a user-centered approach in the field of information retrieval. With the use of design methods such as heuristic UX evaluation, co-sketching, and other original design experiments, the project aimed at identifying the most valuable qualities of physical and digital libraries in order to integrate them within one retrieval system.